The insert molding method is a molding method in which a metal or inorganic solid (hereinafter, abbreviated as metals) is embedded in a resin for utilizing the property of the resin and the material property of the metals. It is applied in wide fields such as automobile parts and electric and electronic parts, and presently one of general molding methods. However, since expansion and shrinkage coefficient (so-called liner expansion coefficient) are extremely different between a resin and metals, molded articles having thin resin portions, portions with large variation in thickness or sharp corners composed of metals, suffer from a lot of troubles such as cracking just after molding and cracking by temperature change in use. Particularly in the case of electric and electronic parts, since high flame-retardance is also required, thermosetting resins such as phenol resins and epoxy resins are widely used for an insert molding.
However, thermosetting resins have disadvantages such as lower productivity due to a long molding cycle and low recycling property, so that substitution with thermoplastic resins is required eagerly.